Corrosion inhibitor-incorporated layered double hydroxide and sol-gel coating compositions and related processes

Abstract

A corrosion-resistant coating on an aluminum-containing substrate such as an aluminum substrate, an aluminum alloy substrate (e.g., AA 2024, AA 6061, or AA7075), or other aluminum-containing substrate includes a corrosion inhibitor-incorporated Zn—Al layered double hydroxide (LDH) layer and a sol-gel layer. A zinc salt and a corrosion inhibitor (e.g., a salt of an oxyanion of a transition metal such as a vanadate) is dissolved to form a zinc-corrosion inhibitor solution, and the substrate is immersed in or otherwise contacted with the solution to form the corrosion inhibitor-incorporated Zn—Al LDH layer on the substrate. A sol-gel composition is applied on the corrosion inhibitor-incorporated Zn—Al LDH layer of the substrate to form a sol-gel layer, and the sol-gel layer is cured.

What is claimed is: 
     
       1. A method for providing a corrosion-resistant coating on a substrate, the method comprising:
 preparing a zinc-corrosion inhibitor solution by dissolving a zinc salt and a corrosion inhibitor, the corrosion inhibitor comprising a salt of an oxyanion of a transition metal; and 
 contacting the substrate comprising an aluminum alloy with the zinc-corrosion inhibitor solution to form a corrosion inhibitor-incorporated Zn—Al layered double hydroxide (LDH) layer on the substrate, wherein the aluminum alloy comprises 2024 aluminum alloy, 6061 aluminum alloy, or 7075 aluminum alloy. 
 
     
     
       2. The method of  claim 1 , wherein the preparing the zinc-corrosion inhibitor solution comprises:
 dissolving the zinc salt in a first aqueous media to form a first solution; 
 adjusting the first solution to a pH ranging from about 6 to about 8; 
 dissolving the corrosion inhibitor in a second aqueous media to form a second solution, the corrosion inhibitor comprising a vanadate, a manganate, a permanganate, a molybdate, a tungstate, or a combination thereof; 
 adjusting the second solution to a pH ranging from about 8 to about 10; and 
 mixing the first and second solution to form the zinc-corrosion inhibitor solution. 
 
     
     
       3. The method of  claim 2 , wherein the dissolving the zinc salt comprises dissolving zinc nitrate in an amount ranging from about 5 to about 30 parts by weight per 100parts by weight of the first solution. 
     
     
       4. The method of  claim 2 , wherein the dissolving the corrosion inhibitor comprises dissolving sodium metavanadate in an amount ranging from of about 0.1 to about 2parts by weight per 100 parts by weight of the second solution, and wherein the zinc-corrosion inhibitor solution has a ratio of a number of moles of zinc to a number of moles of vanadium (n Zn /n V ) ranging from about 5 to about 100. 
     
     
       5. The zinc-corrosion inhibitor solution prepared according to the method of  claim 2 . 
     
     
       6. The method of  claim 1 , wherein the contacting comprises maintaining a pH ranging from about 8 to about 10 and a temperature ranging from about 70 to about 90 ° C. for a time period ranging from about 1 to about 6 h. 
     
     
       7. The corrosion-resistant coating comprising the corrosion inhibitor-incorporated Zn—Al LDH layer formed by the method of  claim 1 . 
     
     
       8. The method of  claim 1 , further comprising:
 contacting a sol-gel composition on the corrosion inhibitor-incorporated Zn—Al LDH layer of the substrate to form a sol-gel layer; and 
 curing the sol-gel layer. 
 
     
     
       9. The method of  claim 8 , further comprising:
 contacting an alkoxysilane with water and an inorganic acid to form a first composition; 
 contacting a zirconium alkoxide with a first organic acid to form a second composition; and 
 mixing the first composition with the second composition to form the sol-gel composition. 
 
     
     
       10. The method of  claim 9 , wherein the contacting to form the first composition comprises mixing the alkoxysilane having the formula R A -Si-(R B ) 3  with the water and the inorganic acid, wherein the R A  is methacryloxyalkyl or glycidyloxyalkyl, and wherein the R B is a methoxy or ethoxy. 
     
     
       11. The method of  claim 9 , wherein the contacting to form the second composition comprises mixing the zirconium alkoxide having the formula Zr-(R c ) 4  with methacrylic acid (MAA), and wherein the R c  is ethoxy, n-propoxy, isopropoxy, n-butyloxy, or tert-butyloxy. 
     
     
       12. The method of  claim 9 , further comprising:
 adding an additional alkoxysilane and MAA to the sol-gel composition, the additional alkoxysilane having the formula R D -Si-(R E ) 3 , wherein the R D  is aryl, aminoalkyl, or glycidoxyalkyl, and wherein the R E  is methoxy or ethoxy. 
 
     
     
       13. The method of  claim 9 , further comprising:
 adding a corrosion inhibiting compound to the sol-gel composition in an amount ranging from about 1 to about 5 parts by weight per 100 part by weight of the sol-gel composition. 
 
     
     
       14. The method of  claim 13 , wherein the adding the corrosion inhibiting compound comprises adding a vanadate, a molybdate, a phosphate, a manganate, a permanganate, a titanate, titania, an aluminate, alumina, ceria, a ceric salt, a cerous salt, or combination thereof. 
     
     
       15. The method of  claim 8 , wherein the curing the sol-gel layer comprises exposing the sol-gel layer to a temperature ranging from about 70 to about 90 ° C. for a time period ranging from about 30 to about 120 min in a hot air circulated oven. 
     
     
       16. The method of  claim 8 , wherein the curing the sol-gel layer comprises exposing the sol-gel layer to infrared (IR) radiation and/or near IR radiation. 
     
     
       17. The method of  claim 8 , further comprising applying primer or paint on the sol-gel layer of the substrate, the sol-gel layer facilitating adherence of the primer or the paint to the substrate. 
     
     
       18. The corrosion-resistant coating comprising the corrosion inhibitor-incorporated Zn—Al LDH layer and the sol-gel layer formed by the method of  claim 8 . 
     
     
       19. A corrosion-resistant coated product, comprising:
 a corrosion inhibitor-incorporated Zn—Al layered double hydroxide (LDH) layer on an aluminum alloy substrate, the corrosion inhibitor comprising a salt of an oxyanion of a transition metal, wherein the aluminum alloy substrate comprises 2024 aluminum alloy, 6061aluminum alloy, or 7075 aluminum alloy; and 
 a sol-gel layer on the corrosion inhibitor-incorporated Zn—Al LDH layer of the substrate, the sol-gel layer comprising a polymer composite of one or more alkoxysilanes and a zirconium alkoxide. 
 
     
     
       20. The corrosion-resistant coated product of  claim 19 , wherein the sol-gel layer contains a corrosion inhibiting compound comprising a vanadate, a molybdate, a phosphate, a manganate, a permanganate, a titanate, titania, an aluminate, alumina, ceria, a ceric salt, a cerous salt, or combination thereof.